1. Field of the Invention
This invention relates to materials utilized in surgical suturing and particularly surgical wire suturing.
2. Description of the Related Art
Surgical suture wire, as opposed to synthetic plastic or gut suture, is generally utilized in surgery wherein a high degree of holding power and infection resistance is required. Such applications include the repair of bone breaks, replacement of hips, sternum closures after cardiac surgery, closure of peritoneum in infected abdominal wounds (such as is common in battle field situations) and the like. It has accordingly been the practice in some of such applications to utilize high strength, corrosion resistant wire of gages 16-20 of titanium, cobalt-chromium or alloy stainless steel, etc., composition having a high tensile strength. For example, the 1983 ASTM standard F-642 (for Medical Devices) designates the maximum tensile strength for stainless steel wire for tissue fixation of between 210 and 200 ksi for a wire of between 0.01 (0.25 mm) to 0.05 (1.25 mm) inch diameter with an elongation of between 8-10%. Cobalt-chromium alloy flexible wire for bone fixation (ASTM F 644) in an 0.01 (0.25 mm) to 0.025 (0.63 mm) inch diameter has a tensile strength of about 185 to 165 ksi with an elongation of 35-40%. These wires, though considered to be flexible, are however, because of their very strength, relatively stiff compared to other suture materials such as of plastic. Accordingly, they are difficult to handle and cannot be readily manipulated to conform to bone surfaces or for exact placement in tissue fixation. Additionally, the stiffness of the wire may result in increased breakage of such wire during and after surgery. Incidence of breakage is further exacerbated with the use of wire tighteners such as disclosed in U.S. Pat. No. 4,527,554. Such wire tighteners prevent the application of marring stress on the wire by providing a movable surface against which the wire ends are biased during the tightening procedure. However, while they form nearly perfect helical ties without marring of the wire (and the formation of weak points), they concentrate stress at the base of the twisted connection. This concentrated stress can be detrimental to the shear, rather than tensile strength of the currently utilized relatively stiff suture wires. Another drawback encountered with the use of small diameter and the relatively stiff wires is that they have the cutting power of a cheese slicer with resultant tissue trauma, particularly if the wire connection is overtightened. Nevertheless, their use has been widespread because it has mistakenly been universally thought that these particular applications require high strength, stiffness and hardness.
In order to minimize tissue trauma and necrosis and infection resulting from overtightening and the "cheese cutter" effect, surgeons may tend to undertighten. Such compensation is however very detrimental, particularly with respect to approximation of the sternum following open heart surgery since undertightened sutures result in sternal "click", a detrimental condition caused by movement of one half of the sternum with respect to the other half, upon coughing or deep breathing. This causes the patient to avoid these maneuvers, thereby resulting in atalectasis and possibly pneumonia.